The invention relates to an arrangement for preventing overfill of an anaesthetic liquid container, comprising means for guiding anaesthetic liquid to the anaesthetic liquid container for vaporization and for removing a volume of gas equivalent to the filling of anaesthetic liquid from the anaesthetic liquid container.
In order for anaesthetic vaporizers functioning on the bypass-saturation principle to operate correctly, the amount of liquid in the liquid container should not exceed an allowable level. If the level should be exceeded, the liquid might block the flow conduit which passes through the liquid container and carries the gas flow to be supplied to the patient. The gas flow can, however, pressurize the liquid container, forcing thus extra liquid out, which results in serious over-administration. For the above reasons, to limit the amount of liquid, vaporizers are provided with a device which prevents them from being filled over the maximum allowable amount of liquid.
The filling of the liquid container of an anaesthetic vaporizer is based on the exchange of volumes in the vaporizer and the supply container for liquid. When liquid flows into the vaporizer, an equivalent volume of gas flows out of it. Correspondingly, when liquid flows out of the supply container, an equivalent volume of gas flows into it. The filling of the vaporizer stops if either or both of the replacement gas flows is/are exhausted.
There are three different types of systems for filling vaporizers: funnel, filler and tube.
In a funnel-type system the anaesthetic liquid is poured from the supply container, i.e. a bottle, to the funnel openly through the external atmosphere. The filling of the container stops, when the liquid surface closes the opening of the funnel that faces the vaporizer, and the gas flow is prevented from flowing out of the vaporizer. Such a system is described, for example, in British Patent No. 1,224,478.
A filler-type system is used to connect the vaporizer and the bottle to each other. In this case, the filling system is closed, and anaesthetic liquid is not allowed to vaporize to the external atmosphere. The filler comprises two tubes: one carries liquid from the bottle to the vaporizer, and the other carries gas from the vaporizer to the bottle. The filler is also standardized, e.g. prEN 1280. The filling of the container stops when the vaporizer is filled to such an extent that the liquid surface reaches the gas conduit.
The tube-type system is also a closed system. In this system, the filling head of the bottle is placed in a filling device provided in the vaporizer. A tight conduit is thus formed between the bottle and the vaporizer, and the valves in both the bottle and the vaporizer are opened. Such a system is disclosed, for example, in PCT publications WO 92/12753 and WO 95/08361. The filling stops when the vaporizer is filled such that the liquid surface reaches the upper edge of the tube.
The solutions described above have the common feature that they are all positioned on a side of the vaporizer. The vaporizer can thus be overfilled if it is tilted in such a way that the edge facing the filling device rises relative to the liquid container. If the filling device falls below the liquid container as a result of tilting, the filling will stop too soon, which does not represent a safety risk in the operation of the device.
Finnish Patent No. 94097 provides a solution for the problem described above. According to this solution, the liquid conduit is provided with an inclined portion in which a ball is positioned. When the vaporizer is tilted such that the filling device rises above the liquid container, the inclination direction of the inclined conduit changes, and the ball in the conduit rolls to a sealing surface at the other end of the conduit, closing thus the liquid flow conduit. This solution is particularly suitable for filler-type devices, in which the liquid and gas flow in opposite directions in separate conduits. It is not suitable for arrangements in which the liquid and gas flow in the same conduit.